If I were David Tennant and found myself having to choose between Alice Eve and Kelly Macdonald, as he must do in The Decoy Bride, I'd, well … there's really no argument, is there?

No disrespect to Alice Eve, but I've been watching Kelly Macdonald for 16 years and somehow it just keeps getting more and more rewarding, especially in the last few, as she's broken out of second-tier parts and started taking more leads. She brings a steely kind of mildness to many of her roles, a quality – to my eye, a very Scottish quality – few other prominent actresses have: everything held back, the eyes giving it all away, the impression of great forces clashing inside what appears to be a tiny, vulnerable frame. She reminds me of what Tom Wolfe said of Joan Didion as a reporter; about being so small, frail-seeming and nervous that powerful figures were so disconcerted that they sometimes blurted out their darkest secrets to her, just to fill the air with something, anything. Maggie Smith and half the cast did that about 10 times to Macdonald in Gosford Park, of which she is the unheralded star.

Not that Macdonald started out all meek and mild. If anything, her career has been overshadowed by her boldly atypical debut in Trainspotting as a sexually audacious underage schoolgirl, who knocks a swaggering Ewan McGregor off his stride and into her bed, and who howls at us from the movie's iconic poster wearing a next-to-nothing sequinned dress. Nothing much like that in the years since, though.

If anything, in fact, there is a chasteness to Macdonald that reminds me of certain Japanese actresses of the 50s and 60s, particularly Yasujiro Ozu's muse, Setsuko Hara, the daughter-mother-sister archetype of so many of his infra-ordinary family dramas. Each of them, with their similarly kindly faces, is deft with the smaller, mundaner emotions, the little momentary dambursts of feeling, suppressed or redirected, or more rarely, submitted to.

But don't let chasteness or meekness blind us to that steel, which was uncovered in State Of Play and, in a different way, in The Girl In The Cafe, a bad movie that needed Macdonald without ever quite earning or deserving the things she managed to do for it. In No Country For Old Men, she was at her most vulnerable, but remained the last unbreakably honest person in that movie's harsh moral universe. Then Macdonald finally got a richly conceived lead role in Boardwalk Empire, where she was at leisure to unwrap, week by week, her increasingly complex and contradictory character: an Irish widow of modest demeanour who may yet prove as Machiavellian as her mobbed-up boyfriend.

Deceit, betrayal, venality and manipulation – oh, I like this new Kelly Macdonald. But I'll never forget she once also played Peter Pan, and was perfectly cast in that role, too.